Conventional methods for converting analog stroke display signals to raster display information for developing a raster-scan image display are considered well known. Some of these conventional conversion methods including elements and processes typically involved in common stroke-type and raster-type systems are described in U.S. Pat. No. 6,496,160, issued to Tanner et al. Such conventional conversion methods, elements, and processes are omitted from the following description for simplicity purposes but are nonetheless incorporated herein by reference.
As mentioned in the Tanner et al patent, because large numbers of stroke display systems had been installed in the past and many are still in use today (for example, stroke display systems are common in commercial and military aircraft), it has been found desirable, when upgrading an existing stroke display system, to save as much of the existing circuitry as possible, especially the stroke generator circuitry. As a result, stroke-to-raster converters have been developed to enable use of the stroke generator, but to convert the stroke generation signals to raster producing signals for use on a raster display device. In effect, a raster display replaces the stroke display to develop the desired images.
In contrast to the problem encountered and solved in the Tanner et al patent when performing a typical stroke-to-raster video conversion, significantly different problems have been frequently and consistently identified by the present inventors. Namely, as the As the X and Y deflection signals draw a symbol the Bright-Up (BU) signal is high. When the symbol is finished being drawn the BU signal drops to zero and the X and Y deflection signals “fly to” their next position to draw the next symbol. The problem exists when the fall-time of the BU signal causes a number of X and Y samples to be displayed as valid image data. These extra pixels, or “tails”, are displayed as a loose string of dots rather than a line. This is because the X and Y deflection signals change at a much higher rate during the “fly to” time. The opposite can also (or instead) happen. That is, the slow rise-time of the BU signal can cause some pixels of the next symbol to be missed and therefore not be displayed at all.
It is therefore desirable to provide a method of performing stroke-to-raster video conversion having leading-edge error correction and/or falling-edge error correction, and that does not suffer from the above drawbacks.
These and other advantages of the present invention will become more fully apparent from the detailed description of the invention hereinbelow.